chapter 8

2 types of sex determination

2 types of sex determination

1. genotypic sex determination

2. temperature dependent sex determination

bipotential gonad

indifferent gonad that could be turned into either the testes or ovaries

what type of sex determination do amphibians have

genotypic sex determination

1. XX/XY

2. ZZ/ZW

heterogamety

when the sex chromosomes are different

ex: male mammals are XY

what type of heterogamety is the ancestral condition and which has evolved

ancestral: female

evolved multiple times: male

reproductive cycles (2)

1. seasonal reproduction

2. aseasonal reproduction

seasonal reproduction

most species in temperate zones

1. only in later winter, early spring

2. only during summer

3. only during autumn

in tropics: wet season breeders (temperature and rainfall)

aseasonal reproduction

continuous reproductive cycles

some anurans in relatively aseasonal tropical habitats

spermatophores in salamanders

males

like a capsule left behind:

1. made of cloacal glands

2. outer layer is a mass of sperm cells

internal fertilization: promotes female parental care

how can female salamanders store sperm

with the spermathecae

1. tubules in wall of cloaca

sperm is stored for later fertilization

amplexus in anurans (3)

mating behavior in which male frog grasps the female from behind to bring their cloacae into close proximity and aid fertiliztion

1. inguinal amplexus

2. axillary amplexus (majority of anurans)

3. cephalic amplexus

which amplexus type is the ancestral condition

inguinal amplexus

which type of amplexus is only found in dendrobatids (poison dart frogs)

cephalic amplexus

nuptial pad in anurans

assists in amplexus for the male to grasp the female more firmly

phalloduem function

caecilians

extension of male cloaca that assists in internal fertilization

hybridogenesis

genome of the female parent that passes unchanged from one generation to the next

paternal genome discarded and gametes produced by hybrid female contain only maternal genome

intermediate phenotype = hybrid female + parental species male

kleptogenesis and the 3 possibilities

females that steal genomes from males of other species

has 3 outcomes:

1. sperm initiates development of embryo but sperm’s genetic material is not incorporated into embryo

2. sperm sometimes incorporates but resulting offspring has a higher ploidy (chromosomes) level

3. sperm genome replaces one of the original genomes in the hybrid offspring

ex: ambystoma species

oviparity in caecilians (2)

1. aquatic larvae

2. direct development with female as parental care

viviparity in caecilians

yolk and maternal secretions

11-12 months

modes of oviparity in salamanders (3)

1. mode 1: pond breeding

2. mode 2: stream breeding

3. mode 3: nonaquatic eggs (has several subcategories)

egg sacs of salamanders in mode 1

pond breeding

more clustered together in a giant ball

egg sacs of salamanders in mode 2

stream breeding

more tube like sacs that are attached to substrate

egg sacs of salamanders in mode 3

terrestrial eggs

laid in shallow depressions or attached to leaves

direct development with no water required or a small amount of water

viviparity in salamanders

very limited

1. some populations where female fertilizes multiple eggs

2. some populations with few eggs and unfertilized ones get eaten by fertilized ones (offspring)

3. some populations with only 2 eggs fertilized

ex: european fire salamander

types of oviposition in anurans (5)

1. various arrangements of independent eggs

2. 3D arrangements

3. floating arrangements

4. foam nests

5. linear arrangements

eggs and larvae in water (anurans)

ancestral form

cluster of eggs in water with arrangement dependent on O2 levels

1. cold: more O2, more clumped together

2. warm: less O2, film of eggs in single layer on top of water

foam nests (anurans)

mucus mixed with water and the frog paddles its feet to foam it

shift from ponds and streams (anurans)

avantages:

1. less predators

disadvantages:

1. less food

offspring subsist on yolk in eggs instead

aboreal water (anurans)

tree holes

ex: bromeliads where a single egg gets places in the direct center

eggs on land where larvae develop in water (anurans)

mud nests, water sac on bottom of leaf

rain breaks mud nest open

in water sac, eggs are out of predators way and they simply drop out when ready

non aquatic larvae (anurans)

direct development where development occurs entirely in the egg

no metamorphosis (tadpole stage)

ex: australian turtle frog

parental care in anurans (4)

1. egg attendance

2. transport of eggs

3. attendance of tadpoles and/or young

4. transport of tadpoles and/or young, and feeding of tadpoles

ex of a frog that transports its tadpoles

dendrobatids

transport tadpoles from terrestrial oviposition site to a body of water

viviparity in anurans (2)

1. lecithotrophy

2. matrotrophy

includes 9 species between the 2 types

lecithotrophy

yolk reserves

7 species

matrotrophy

maternal secretions

2 species

benefits of direct development and viviparity in anurans (2)

1. large eggs, large yolk reserves

2. not dependent on standing water

costs of direct development and viviparity in anurans (3)

1. reduction in total reproductive output

2. lower clutch size

3. increased vulnerability to predation

benefits of parental care in anurans (4)

1. decrease in pathogens (cleaner eggs)

2. decrease in predation

3. increase in aeration

4. prevents desiccation (keeps moisture)

costs of parental care in anurans (3)

1. reduced reproductive output

2. decrease food intake

3. reduced survival of the parent

what is the relationship between egg size and clutch size (anurans)

quality: larger egg size, smaller clutch size

• direct development, parental care

quantity: smaller egg size, larger clutch size

• species that lay eggs water, aquatic larval development

how does resource variability influence egg and clutch size (anurans)

excess food:

• larvae hatch from large eggs, metamorphose sooner in larger in size

limited food:

• larvae hatch from small eggs, metamorphose earlier

how does environmental variability influence egg and clutch size (anurans)

favorable environment:

• small eggs might survive, female could increase fitness by producing many small eggs

unpredictable environment:

• produce a range of egg sizes that might increase the change that some offspring will survive

larval development in caecilians

no aquatic larval stage

those with aquatic stage are relatively short and their external gills are lost quickly

larval development/metamorphosis in salamanders

pond dwelling larvae keep tail fin and lateral line

stream dwelling larvae lose tail fin and lateral line

lateral line in pond dwelling salamander larvae

a line of sensory receptors

larval development/metamorphosis in anurans (4)

1. egg fertilized

   • external gills develop

2. early stage: tadpoles subsist largely on yolk in

   • mouth development

3. late stage: tadpoles feed (are herbivores)

   • limb development

4. adult stage: primarily carnivorous

how can environmental variation alter life history traits in anurans

breeding in rain pool vs longer lasting temporary pond vs longer lasting pond has effects on duration of larval stage

rain pool: shortest (8 days)

longer lasting pond: longest (7 weeks)

how does larval body size > minimum body size trigger either additional growth or metamorphosis in the wilbur collins model

not >: additional growth

yes >: decide if larval body size > max body size

how does larval body size > maximum body size trigger either additional growth or metamorphosis in the wilbur collins model

not >: size specific growth rate

yes >: metamorphosis

how does size specific growth rate trigger either additional growth or metamorphosis in the wilbur collins model

not: metamorphosis

yes: additional growth

how does population density influence growth in anurans

smaller density: grow larger

higher density: grow smaller (competition)

how can environmental varation (duration of aquatic environments) influence the expression of paedomorphosis

shorter duration (temporary pond): less paedomorphic

longer duration (longer lasting pond): more paedomorphic

how can environmental variation (absence of light) influence the expression of paedomorphosis

more paedomorphic in cave dwelling (light absence) species